100% certified pure. They use a scale and fill my 50# tank right in front of me. When I get home and hook it up, and let it sit untill it reaches room temp, and its always at 3300psi to 3400psi depending on the room temp. The psi will be at that no matter how much co2 is in the tank. It won't drop below that until it is out. I've tried several other methods of co2 generation, and none have compared to this. The only downfall is lugging a tank around every couple weeks. The company I go to will lease tanks up to 1000# and come fill them for half the cost of doing a small 50# tank. The biggest benefit is no heat generated by propane generators, and no co2 bags hanging everywhere.